Home on the Range has court-accepted dates, since the Goodwin claim died in 1934 with the discovery of a printed copy from 1876.
I think Waltzing Matilda fell into that 1923 catch-22 because the words, although written near the end of the 19th c, , and the music as well, were changed somewhat in the version most used. It is that version that is copyrighted. (Too lazy to go back to the threads on this which have a clickee to an Australian site with the whole story).

I think anyone would have a hell of a time trying to claim copyright on Ida Red-Cripple Creek. Most of the words can be traced to verses collected around 1915 by various collectors. Sharpe had the tune. Brown has "Cripple Creek sung in two versions, with music, before 1923. The Poole and Wills versions, however, are protected in their unique form.

I would like to have this provision of the Copyright Law fleshed out with examples- and this is where your question comes in-
Quoting from the regulations- "Works originally created before January 1, 1978, but not published or registered by that date.
These works have been brought automatically under the statute and are now given federal copyright protection. The duration of copyright in these works will generally be computed in the same way as for works created on or after January 1, 1978: the life + 70 or 95-120 year terms will apply to them as well. The law provides that in no case will the terms of copyright for works in this category expire before December 31, 2002 and for works published on or before December 31, 2002, the term of copyright will not expire before December 31, 2047."

I can't get a clear picture in my head here. What is the starting date under this section? Is it the date of registration or publication? Or is it some date of origin, determined from notes or some other way?
Legal help, please. Not the first time that this has come up, but never answered satisfactorily.
Interesting point. You can register a diary, etc., found in your grandmother's attic if you are the legal heir.
US Copyright Regulations- US Copyright